To copy files between VMs to the host, I sometimes create an image in VHD format and treat it like a "SHARE disk".

1. create a VHD image with virtualbox2. format the disk in the VM (I usually go for ext4 or fat32)3. copy files and close the VM4. mount the VHD image via windows disk management tool5. assign letter to the partition6. move the files elsewhere

I use "Ext2Fsd" to assign the volume letter if the partition contains ext4 file system.